The dual-function impeller can be rotated in molten metal in a direction of rotation, as part of a rotary injector. The impeller can have a body having an axis, a plurality of blades circumferentially interspaced around an axis, and an aperture coinciding with the axis. The blades having both a radially extending portion facing the direction of rotation and collectively generating a radial flow component upon said rotation, and a slanted portion also facing the direction of rotation, inclined relative to a radial plane, and collectively generating an axial flow component directed away from the rotary injector upon said rotation.